Single-use, disposable bioreactor vessels use a bag as opposed to a more expensive reusable culture vessel. The bag itself is typically made of a flexible plastic, but may be encased in a structure such as a rocker or a cuboid, or cylindrical steel support depending upon the experiment or reaction process under analysis. Commercial, single-use bioreactors have been available for over a decade and are now available from several manufacturers. Such bags commonly include one or more “ports” enabling the contents of the bag to be sampled and monitored.
Raman spectroscopy has become a powerful tool for use in conjunction with in situ process analysis. Sophisticated fiber-optic coupled Raman probes are now routinely used for process sampling in various industries, including bioreactor applications. It would be highly advantageous to couple a Raman probe to a bioreactor bag, through an available port, for example, but a tradeoff exists between the expense and complexity of the probe versus the bag assembly, which is designed to be disposable. Certainly the Raman probe itself cannot be disposable. Nonetheless, if certain components of the probe are not precisely aligned within the port, the required accuracy, repeatability, and reaction model transferability between reaction batches and probes will not be achieved.
There have been attempts to provide for disposable couplings to bioreactor vessel ports, but these attempts do not facilitate precise Raman sampling. U.S. Pat. No. 8,008,065 for example, discloses a port and sensor assembly adapted for use with an optical fiber-based phase fluorometric or Raman measurement system. A fiber or fiber bundle used as the excitation light source is anchored into a disposable insert shell through a ferrule or other suitable retention system. The diverging light from the fiber or fiber bundle is preferably collimated using a lens or lens system so that the collimated light is incident on a fluorescent dye spot. The fluorophore absorbs the excitation light and emits a fluorescent signal that impinges upon a collection system which is focused returned to a photo-diode through the same lens and fiber or fiber bundle. The fluorescent dye spot and fiber are mounted in a disposable shell that is inserted into a port affixed to the disposable bioreactor's lining.
While the system just described provides for a limited degree of fluorescence detection, it does not accommodate the exacting focusing requirements demanded of a state-of-the-art Raman sampling probe. Efficient and repeatable Raman sampling in a variably turbid sample medium, such as a bioreaction, requires the probe to be focused at a very short depth into the turbid sample from a disposable port window. Too deep a focus can negatively impact both the strength and the shape of the measured Raman spectrum.